The present invention pertains to a sewing unit for automatically joining lengths of cloth, of the type that includes a conventional sewing machine having the usual needle and feed mechanism that defines the sewing axis along which said lengths of cloth are fed in order to be joined.
The known forms of sewing units are usually equipped with a guide that consists of superimposed blades that are disposed in spaced relation so as to define channels between which the lengths of cloth to be joined are positioned and slidable.
These sewing units also have auxiliary devices that travel with the cloth, such as an end and an intermediate gripper, which serve to keep the superimposed edges to be sewn aligned and taut.
The spaces between the blades defining the guide channels are slightly greater than the thickness of the cloth, so as to prevent the cloth from bunching in said channels during the sewing operation.
One drawback of using such guides is that they obstruct the free sliding movement of the cloth when there are intersecting seams in the workpiece or thicker areas due to the application of pockets or the like.
The problem is particularly acute with regard to the sewing of trouser-leg seams when the crotch seam, which intersects the inside seam, is located forwardly of the guide.
More specifically, the problem is more pronounced when the fabric is of lightweight construction and very pliable. To provide the sewing unit with guides having adequate channels to permit passage of the intersecting seams results in an excessive freedom of movement of the cloth causing the latter to fold on itself and the intended aligning action of the guides on the superimposed edges is lost.
The same problem arises, for example, when knitted garments or tops with sleeves are to be joined with the sleeve-joint seam during the closing of the sleeve or the relevant side which procedure is normally performed in one continuous operation.
This problem has already been resolved in those cases where the seam that intersects the joining seam or the thicker areas is very close to the point where the joining seam begins as, for example, in the case of the joining of trouser quarters with a pocket (already attached).
The solution for such cases provides a movable work guide, located adjacent the sewing machine, that is attached to the lengths of cloth to be joined, after said intersecting seams or thicker areas have been sewn.
The guiding action on these lengths of cloth for the short distance involved with regard to intersecting seams or thicker areas is carried out directly by the presser foot of the sewing machine in conjunction with the guide itself, which is mounted on a suitable rectilinear rail. Advantage was taken of the fact that the edges in such a position fit together and have identical profiles. On the other hand, in the event that the intersecting seams or the thicker areas are substantially spaced from the starting point of the joining seam -- as is the case of trouser crotch seams or the sleeve-joints of knitted garments -- it is not possible to utilize available technology.
An object of the present invention is to facilitate sewing operations of the type described above by means of the use of guides having channels which are proportioned according to the thickness of the lengths of cloth, without having to take into account the areas of greater thickness formed therein. This object is completely accomplished by the automatic unit comprising the present invention.